Concrete member w/ Different Fc'

[MAITO]

good day!

In the design of highrise concrete buildings where the lower level columns have bigger fc' than the top level columns, how do i specify the properties to staad? is it possible to compute for the Ec=4700(fc')^.5 and substitute it that column? or do i have to convert the column section of the lower level by multiplying its modular ratio n=fc'(below)/fc'(above)? which one is more realistic?
any suggestion.

thanks

 

[KRH]

It seems that you are one of the many users who do not read the user manual ! There is a way to input the concrete f'c instead letting the program calculate it.

 

[lippie]

Use the command START CONCRETE DESIGN...after that, you can specify FC x where x is a number. Doing it graphically (which is the way I prefer), is much easier. Staad has a new RC Designer which is fantastic for column, beam and slab design. I found it in 2002...don't know if it is in earlier versions.